Memory controller circuits can be used in a variety of computer systems (e.g., desktop personal computers, notebook computers, personal digital assistants, etc.) to facilitate the computer system's processor in accessing memory chips. For example, a memory controller can have an interface for connecting to one or more synchronous dynamic RAM (SDRAM) chips. The memory controller uses this memory interface to route data between the processor and RAM chips and to send address and control signals to the RAM chips.
A memory controller typically includes a set of control registers to store data needed for operations performed by the memory controller. This data is stored in the control registers so that the data can be changed by the basic input output system (BIOS) or software such as, for example, the operating system (OS) or other driver software.
The data stored in some control registers is hardware protected after being loaded by the BIOS during a hard or full reset operation. For example, some registers store threshold values or settings that are used in controlling a voltage or the temperature of the memory controller. The memory controller protects such registers so that a user or a virus cannot change the values of these thresholds or settings to a level that can cause faulty operation or even damage the chip.
However, this register protection system lacks flexibility in that the values loaded into these protected registers are typically set for a worst-case scenario. For example, the settings may include the duration of a throttling operation when the memory controller's temperature gets too high. This duration would be set for the worst-case heat removal rate. Unfortunately, the memory controller's performance is degraded for the duration of the throttling operation.
In some applications, the heat removal rate can change depending on the application's operational mode. For example, the memory controller may be used in a notebook computer, which can be operated in an undocked mode (i.e., using battery power) or in a docked mode (i.e., docked in a docking station that has its own power source). In the undocked mode, the notebook computer may be configured to turn off a fan to conserve power, resulting a relatively low heat removal rate. Thus, when the fan is off, the throttling duration should be relatively lengthy. In contrast, when the fan is on, the heat removal rate is relatively high and the throttling duration can be shorter. However, because the OS or application software cannot change the data stored in the protected registers by the BIOS after a full reset, the throttling duration is loaded for the worst case (i.e., the duration needed to cool the chip when the fan is off).